1 Field of the Invention
This invention relates to a tens barrel having an electrically-driven diaphragm device.
2. Description of the Related Art
The conventional lens barrel of the kind mentioned above has been arranged, as described in the specification of U.S. Pat. No. 4,326,789, to have the diaphragm device driven by a driving power coming from a camera body through an automatic aperture control lever which is a mechanical interlock member.
FIG. 2 is a vertical section showing a lens barrel of a novel type which has been proposed. Referring to FIG. 2, a guide tube 3 carries a lens L1. The guide tube 3 is provided with a guide slot 3b which extends along an optical axis and a roller 3c which is secured to the guide tube 3. A middle tube 4 carries an optical system which consists of a lens L2 and an electrically-driven diaphragm device 38. A roller 5 is secured to the middle tube 4. A cam tube 28 is rotatably carried by the outer side of the guide tube 3. The cam tube 28 is provided with a cam slot 28a which has the roller 5 inserted into it in such a way as to be movable without rattling. A circumferential slot 28b extends in the circumferential direction of the cam tube 28 in such a way as to have the roller 3c of the guide tube 3 fitted therein and to limit the movement of the cam tube 28 in the direction of the optical axis. A pin 29 which is secured to the cam tube 28 is pinched by a fork-like metal piece 30 in such a way as to revolve together with the fork-like metal piece 30.
In the lens barrel, the fork-like metal piece 30 is arranged to be driven to rotate by a vibratory wave motor M via a rubber ring 21, a rotation transmission ring 22, a differential ring 23, a shaft screw 24 and a roller 25. The cam tube 28 is arranged to be caused by the vibratory wave motor M, via the fork-like metal piece 30, to rotate around the optical axis. When the cam tube 28 is thus rotated, the roller 5 which is fitted in an intersection point between the guide slot 3b and the cam slot 28a is guided to move in the direction of the optical axis together with the middle tube 4.
FIG. 3 is a vertical section showing a conventional lens barrel. Referring to FIG. 3, a middle tube 31 carries an optical system which consists of lenses L1 to L6 and a diaphragm device 38. The middle tube 31 is provided with a thread part 31a on the outer side thereof for drawing the optical system outward. A rotary ring 32 has thread parts formed both on its inner and outer sides and is screwed to a fixed tube 34 by the outer thread part. A key way 31b is formed in the middle tube 31 in parallel to the optical axis. A key 35 which is secured to the fixed tube 34 is fitted without play in the key way 31b. An operation member 33 is unified with the rotary ring 32. A ball bearing 37 is arranged to carry an automatic aperture control lever 36 in such a way as to allow it to freely rotate around the optical axis. A lever 39 is arranged to open or close the aperture of the diaphragm device 38. A mount 40 is provided for coupling with a camera body which is not shown.
When the operation member 33 is rotated in the structural arrangement mentioned above, the rotary ring 32 rotates to act on the middle tube 31 which is screwed to the inner side of the rotary ring 32. Since the key 35 allows the middle tube 31 to move only in the direction of the optical axis, the optical system which consists of the lenses L1 to L6 and the diaphragm device 38 and which is carried by the middle tube 31 is caused by the rotation of the operation member 33 to move in the direction of the optical axis. When a force is exerted from the camera body on the automatic aperture control lever 36, the lever 36 turns around the optical axis O to transmit a turning force to the diaphragm operating lever 39. The aperture of the diaphragm device 38 thus can be opened and closed by the turning movement of the lever 39.
The arrangement of the conventional lens barrel shown in FIG. 3, however, necessitates an arrangement to drive the diaphragm device from the camera body through a mechanical connection member and to move straight the diaphragm device or the lens group including the diaphragm device in the direction of the optical axis. It is of course conceivable to move them by a mechanical connecting arrangement including some rotating movement. However, this method makes the structural arrangement too complex and hardly practicable.
As to the arrangement to move straight the diaphragm device, etc., it is generally practiced to make a forward movement by a double screw arrangement as shown in FIG. 3 or to arrange a cam tube in combination with a guide tube as shown in FIG. 2. However, these methods have presented a problem that they hinder a reduction in size and manufacturing cost of the lens barrel.